It is known that some navigation systems are tracking instrument position during their position adjustment.
It is known that some instruments are adjusted by screws, such as cutting planes of cutting blocks for total knee replacement procedures.
Many devices use screws to adjust and finely tune the position of a surgical instrument. For instance, in U.S. Pat. No. 6,712,824, Millar uses a mechanism with three screws to adjust the plane position of a cutting guide for knee surgery, but the screws must be adjusted manually which takes time. Similar principles can be found in EP 1 444 957 by Cusick, or US 2006/0235290 by Gabriel. Moreover the mechanical architecture in those inventions is serial and it does not lock automatically to a given position when the screws are not turned, it is therefore necessary to lock the screws to a given position with an additional locking screw mechanism or to use additional pins in the bone to fix the cutting guide.
More complex architectures are using more than three screws in order to adjust cutting blocks. For instance, in EP 1 669 033, Lavallee uses a navigation system to adjust the position of several screws of a femoral cutting block but this process is not easy and it takes a long time.
The tracking technology of trackers and navigation systems is independent of the invention, provided that the trackers are tracked in real-time by the navigation system. It includes, but is not limited to optical active technology, with active infrared Light Emitting Diodes (LEDs) on trackers, optical passive technology (with passive retro-reflective markers on trackers), mechanical passive arms with encoders, accelerometers and gyrometers, or magnetic technology. Those tracking technologies are known as prior art of navigation systems for surgery.
Referring to FIG. 1, the instrument 1 is any surgical instrument that has the following characteristics:                [A] The instrument 1 has a tracker 10 attached thereon so that it is tracked by the navigation system 2. The navigation system 2 comprises a camera 20 and a computer 21 with a screen.        [B] The instrument 1 is rigidly fixed to a solid 3 that is also tracked by the navigation system 2.        [C] The instrument has a fixed part 11 which is fixed to the solid 3 and a mobile part 12 which is mobile with respect to the fixed part 11.        [D] The position of the fixed part 11 with respect to the mobile part 12 can be adjusted by screws 13. The number of screws is independent of the invention.        
A screwdriver 7 is used to adjust the instrument position with respect to the solid 3 in a target position. The target position of the instrument is supposed to be selected by the surgeon or set to default values with respect to anatomical landmarks digitized with the navigation system. The target position is represented by a geometric relationship between the fixed part 11 of the instrument and its mobile part 12. By trivial calibration, the target position can be represented equivalently to a geometric relationship between a tracker attached to the mobile part and a tracker attached to the fixed part or to the solid.
The problem is for the user to move several screws 13 independently to move the mobile part 12 until the geometric relationship between the mobile part tracker 10 and the solid tracker 30 matches within a very low tolerance limit such as for instance 0.5 mm and 0.2°.
The manual adjustment of individual screws 13 takes a long time and it is difficult to converge towards a solution.
To help this process, for any initial position of the screws 13 and mobile part 12, the computer 21 of the navigation system 2 can calculate the necessary screw differential adjustments DSi, for each screw 13i (where i is from 1 to N and N is the number of screws), which is necessary to bring the mobile part 12 in the target position. This is an easy calculation that only requires knowing the geometry of the screw placements with respect to the mobile and fixed parts and that is specific to each geometry. In a first step, the display of the navigation system can simply show the adjustments necessary DSi on each screw to the user such that the user follows the indications on the screen. While the screws 13 are manually adjusted, the values DSi are recalculated in real-time and the user can adjust the various screws accordingly.
However, this process remains long and complicated.
The present invention thus aims at providing an adjustment process that is short and simple in order to save intraoperative time.